1. Field of the Invention
The present invention relates to a machining method by which a wafer is divided into individual devices through irradiation with a laser beam.
2. Description of the Related Art
In the semiconductor device manufacturing process, a plurality of regions are demarcated by planned dividing lines, called streets, arranged in a grid pattern on the face side of a substantially circular disc-shaped semiconductor wafer, and devices such as ICs, LSIs, etc. are formed in the thus demarcated regions. Thereafter, the semiconductor wafer is cut along the streets by a cutting apparatus, and the semiconductor wafer is divided into individual semiconductor chips (devices). The wafer to be divided is ground on the back side thereof so as to have a predetermined thickness before being cut along the streets. In recent years, the thickness of the wafer is demanded to be reduced to a smaller value, for example, about 50 μm, in order to achieve reductions in the weight and size of electric apparatuses in which the individual semiconductor chips are used.
The wafer thus made thinner becomes nerveless like paper and difficult to handle, so that the wafer may be broken during its conveyance or the like. To cope with this problem, therefore, a grinding method has been proposed in which the back side of the wafer is ground only in an area corresponding to the device region so as to form an annular reinforcement part on the back side of the wafer in an area corresponding to a peripheral surplus region surrounding the device region (see, for example, Japanese Patent Laid-open No. 2007-173487). In addition, as a method by which the wafer thus formed with the annular reinforcement part at the outer periphery on the back side thereof is divided along the streets (planned dividing lines), a method has been proposed in which the wafer is cut by a cutting blade from the face side after the annular reinforcement part is removed (see, for example, Japanese Patent Laid-open No. 2007-19379).